My cat has recently started peeing on my bed. She only does it on my boyfriends side, yet he has done nothing to upset her. She is young, and in excellent health. This is the only location she has done it. No changes have been made to our home recently, and her litter is clean and the same as always. Other than this she is behaving normally. This clearly seems to be a mental thing, not physical. Any ideas on what could cause this?